题目大意：给你一棵树，返回每一层最大的元素的值。

You need to find the largest value in each row of a binary tree.

Example:

<b>Input:</b> 

          1
         / \
        3   2
       / \   \  
      5   3   9 

<b>Output:</b> [1, 3, 9]

Solution 1: Inorder traversal + depth info

C++

// Author: Huahua
// Running time: 15 ms
class Solution {
public:
  vector<int> largestValues(TreeNode* root) {
    vector<int> ans;
    inorder(root, 0, ans);
    return ans;
  }
private:
  void inorder(TreeNode* root, int d, vector<int>& ans) {
    if (root == nullptr) return;
    while (ans.size() <= d) ans.push_back(INT_MIN);    
    inorder(root->left, d + 1, ans);
    ans[d] = max(ans[d], root->val);
    inorder(root->right, d + 1, ans);
  }
};

Python3

"""
Author: Huahua
Running time: 72 ms (beats 100%)
"""
class Solution:
  def largestValues(self, root):
    def inorder(root, d, ans):
      if not root: return ans
      if len(ans) <= d: ans += [float('-inf')]
      inorder(root.left, d + 1, ans)
      if root.val > ans[d]: ans[d] = root.val
      inorder(root.right, d + 1, ans)
      return ans
    
    return inorder(root, 0, [])

The post 花花酱 LeetCode 515. Find Largest Value in Each Tree Row appeared first on Huahua's Tech Road.